docs: def _read_pdb(path):
          """Read PDB file from local drive."""
          r_mode = 'r'
          openf = open
          if path.endswith('.gz'):
              r_mode = 'rb'
              openf = gzip.open
          with openf(path, r_mode) as f:
              txt = f.read()
          if path.endswith('.gz'):
              if sys.version_info[0] >= 3:
                  txt = txt.decode('utf-8')
              else:
                  txt = txt.encode('ascii')
          return path, txt